Changing the direction of a pipeline from essentially horizontal to essentially vertical is a common problem in many areas, one such area being the offshore oil industry where a pipeline running horizontally along the ocean floor must be directed to an essentially vertical orientation so as to connect with some surface facility such as a drilling or production platform. These pipelines usually carry hydrocarbons under pressure and it is therefore desirable to have a continuous pipe to avoid problems associated with subsea connections. Techniques currently known to the industry to perform such connections include the "Bending Shoe Method"; the "Open J-Tube Pull"; the "J-Tube Method"; and the "Reverse J-Tube Method".
The "Bending Shoe Method" of installation involves the positioning of the pipeline on the sea bed and extending it past the platform. The free end of the pipeline is then pulled by a winch on the platform against a "bending shoe" a support of fixed radius near the base of the platform, until the pipeline is bent into a vertical position.
A variation of the bending shoe method involves pulling the pipe past and against the bending shoe to the surface. This is sometimes referred to as an open J-tube pull. The J-tube pull method involves connecting a cable threaded through a preinstalled J-tube from the platform to a pull head on the leading end of the pipe. The cable is connected to a surface crane or pulling winch mounted on the platform. The pipeline is then pulled through the J-tube to the surface.
In the reverse J-tube method, the pipe is initiated at the platform deck and lowered through the J-tube. The pipe is held in position and fed into the J-tube by a gripper machine on the platform deck. If a downward pulling force is needed on the pipe, a cable may extend from the pull head on the pipe, down through the J-tube to exit at the bottom thereof and connect to a pulling winch at the surface. The pull force may be provided by a derrick or a pipe lay barge or by another pulling arrangement.
In all of the above mentioned known methods, the radius of curvature of the bending shoe or J-tube is kept large, relative to the diameter of the pipe being bent, in order to keep deformation of the pipe low, typically 2% permanent strain or less. This results in a large cumbersome J-tubes and bending shoes particularly as the pipe diameter increases. The use of the present invention allows the use of J-tubes of smaller radius of curvature while maintaining the intregrity of pipe installed through one such J-tube.